Serous and Mucinous Cystic Neoplasms of the Pancreas

Cystic neoplasms of the pancreas are uncommon tumors and are seen in less than 5% of pancreatic neoplasms. Pancreatic cystic neoplasms are classified into two categories, serous cystic (usually microcystic, occasionally unilocular) neoplasms that are benign, and mucinous cystic (macrocystic) neoplasms that are potentially malignant or already malignant at the time of diagnosis. There is a rare macrocystic variant, which is benign and exhibits radiological features similar to those of mucinous cys-tadenoma. Serous and mucinous cystic neoplasms, except for intraductal papillary mucinous tumors (IPMT) do not communicate with the pancreatic duct.

Serous cystic neoplasms of the pancreas are observed in middle-aged and elderly women. This type of tumor rarely requires surgical treatment, whereas mucinous cystic tumors should be resected because of their malignant potential. Nevertheless, some surgeons prefer to resect the serous type as well. In general, the patient's age, overall condition, location of the lesion, and growth over time are factors that help in deciding if surgery is needed [34]. Often any cyst that increases in size, any symptomatic cyst, and cysts in older fit patients are selected for surgery. CT can accomplish preoperative differentiation of the two types in many cases. In serous cystic tumors, traditionally the diagnosis is made if the number of cysts within the tumor is more than six and the diameters of the cysts less than 2 cm [35, 36]. A newer nomenclature calls cysts < 1 cm definitely serous, > 1-2 cm equivocal and > 2 cm definitely mucinous. Grossly, these serous tumors appear either as solid tumors with innumerable tiny cysts, or as honeycombed cystic tumors, depending on the amount of connective tissue. They have a lobulated margin. At times, it is difficult to visualize the cystic areas. Calcifications in serous tumors are central in location and more common than in mucinous tumors. A central enhancing scar may be present and is characteristic of a serous tumor [13].

Mucinous cystic neoplasms of the pancreas (also called cystadenomas and cystadenocarcinomas according to the old nomenclature) have six or fewer cysts, the diameters of the cysts measure more than 2 cm, a central enhancing scar is rarely seen, and calcifications are peripheral [13] (Fig. 3). The margins usually are smooth, and metastatic disease may be present at the time of diagnosis.

Based on the above-mentioned criteria, a correct diagnosis of a serous cystic pancreatic tumor can be made in

Fig.3. Thin-section MDCT of serous cystic neoplasm of the pancreas, pancreatic phase. A lobulated and septated cystic mass is present in the body of the pancreas (arrows). The individual cysts are small

62% of cases by CT, in 74% by sonography and in 84% using both modalities [35]. In general, results for mucinous cystic tumors are inferior. Pancreatic pseudocysts and cystic forms of islet cell tumors, ductal carcinomas, solid and papillary tumors and lymphangioma of the pancreas can be indistinguishable from cystic neoplasms on CT. Thus, needle biopsies of the lesions often are necessary.

MRI often can provide better definition of the internal architecture of these cystic neoplasms than CT. Septa and wall thickness of the lesions are well demonstrated by MRI, but calcifications are not always seen. Also, differentiation between serous and mucinous compartments is superior by MRI. MRI is of great help in distinguishing these cystic neoplasms from pseudocysts of the pancreas, particularly if they are multiple. Both MRCP and MDCT with curved planar reconstruction can demonstrate the absence of a connection to the main pancreatic duct.

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